* [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set
@ 2017-08-08 17:20 Neeraj Upadhyay
2017-08-08 18:02 ` Paul E. McKenney
0 siblings, 1 reply; 4+ messages in thread
From: Neeraj Upadhyay @ 2017-08-08 17:20 UTC (permalink / raw)
To: paulmck, josh, rostedt, mathieu.desnoyers, jiangshanlai
Cc: linux-kernel, Neeraj Upadhyay
If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall()
does checks to figure out whether jiffies is past rsp->jiffies_stall,
doing ordered accesses to avoid any false positives for new grace
period initialization after a sufficiently large idle period. This
extra processing can be skipped if rcu_cpu_stall_suppress is set.
Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS")
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
---
kernel/rcu/tree.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 51d4c3a..91b7552 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
unsigned long js;
struct rcu_node *rnp;
- if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
- !rcu_gp_in_progress(rsp))
+ if (!rcu_gp_in_progress(rsp))
return;
rcu_stall_kick_kthreads(rsp);
+
+ if (rcu_cpu_stall_suppress)
+ return;
+
j = jiffies;
/*
--
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a
member of the Code Aurora Forum, hosted by The Linux Foundation
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set 2017-08-08 17:20 [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set Neeraj Upadhyay @ 2017-08-08 18:02 ` Paul E. McKenney 2017-08-08 18:57 ` Neeraj Upadhyay 0 siblings, 1 reply; 4+ messages in thread From: Paul E. McKenney @ 2017-08-08 18:02 UTC (permalink / raw) To: Neeraj Upadhyay Cc: josh, rostedt, mathieu.desnoyers, jiangshanlai, linux-kernel On Tue, Aug 08, 2017 at 10:50:26PM +0530, Neeraj Upadhyay wrote: > If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall() > does checks to figure out whether jiffies is past rsp->jiffies_stall, > doing ordered accesses to avoid any false positives for new grace > period initialization after a sufficiently large idle period. This > extra processing can be skipped if rcu_cpu_stall_suppress is set. Just to make sure I understand, the concern is that someone might have booted with rcupdate.rcu_cpu_stall_suppress=1 (thus suppressing the RCU CPU stall debugging warnings implemented later in check_cpu_stall()), but later decided to also boot with rcutree.rcu_kick_kthreads=1 (thus enabling kicking kthreads which check for RCU's grace-period kthreads not being properly awakened)? My immediate reaction is that if there is not much point in specifying both rcutree.rcu_kick_kthreads=1 and rcupdate.rcu_cpu_stall_suppress=1. But is there some use case that I am missing? Thanx, Paul > Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS") > Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> > --- > kernel/rcu/tree.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 51d4c3a..91b7552 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) > unsigned long js; > struct rcu_node *rnp; > > - if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || > - !rcu_gp_in_progress(rsp)) > + if (!rcu_gp_in_progress(rsp)) > return; > rcu_stall_kick_kthreads(rsp); > + > + if (rcu_cpu_stall_suppress) > + return; > + > j = jiffies; > > /* > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set 2017-08-08 18:02 ` Paul E. McKenney @ 2017-08-08 18:57 ` Neeraj Upadhyay 2017-08-08 21:56 ` Paul E. McKenney 0 siblings, 1 reply; 4+ messages in thread From: Neeraj Upadhyay @ 2017-08-08 18:57 UTC (permalink / raw) To: paulmck; +Cc: josh, rostedt, mathieu.desnoyers, jiangshanlai, linux-kernel On 08/08/2017 11:32 PM, Paul E. McKenney wrote: > On Tue, Aug 08, 2017 at 10:50:26PM +0530, Neeraj Upadhyay wrote: >> If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall() >> does checks to figure out whether jiffies is past rsp->jiffies_stall, >> doing ordered accesses to avoid any false positives for new grace >> period initialization after a sufficiently large idle period. This >> extra processing can be skipped if rcu_cpu_stall_suppress is set. > Just to make sure I understand, the concern is that someone might have > booted with rcupdate.rcu_cpu_stall_suppress=1 (thus suppressing the RCU > CPU stall debugging warnings implemented later in check_cpu_stall()), > but later decided to also boot with rcutree.rcu_kick_kthreads=1 (thus > enabling kicking kthreads which check for RCU's grace-period kthreads > not being properly awakened)? > > My immediate reaction is that if there is not much point in specifying > both rcutree.rcu_kick_kthreads=1 and rcupdate.rcu_cpu_stall_suppress=1. > But is there some use case that I am missing? > > Thanx, Paul For boot time configuration, agree, there isn't much point in enabling both options. In addition to boot time, rcu_cpu_stall_suppress can be temporarily enabled during some operations like sysrq; but this may not be a use case worth consideration. > >> Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS") >> Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> >> --- >> kernel/rcu/tree.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c >> index 51d4c3a..91b7552 100644 >> --- a/kernel/rcu/tree.c >> +++ b/kernel/rcu/tree.c >> @@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) >> unsigned long js; >> struct rcu_node *rnp; >> >> - if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || >> - !rcu_gp_in_progress(rsp)) >> + if (!rcu_gp_in_progress(rsp)) >> return; >> rcu_stall_kick_kthreads(rsp); >> + >> + if (rcu_cpu_stall_suppress) >> + return; >> + >> j = jiffies; >> >> /* >> -- >> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a >> member of the Code Aurora Forum, hosted by The Linux Foundation >> -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set 2017-08-08 18:57 ` Neeraj Upadhyay @ 2017-08-08 21:56 ` Paul E. McKenney 0 siblings, 0 replies; 4+ messages in thread From: Paul E. McKenney @ 2017-08-08 21:56 UTC (permalink / raw) To: Neeraj Upadhyay Cc: josh, rostedt, mathieu.desnoyers, jiangshanlai, linux-kernel On Wed, Aug 09, 2017 at 12:27:16AM +0530, Neeraj Upadhyay wrote: > > > On 08/08/2017 11:32 PM, Paul E. McKenney wrote: > >On Tue, Aug 08, 2017 at 10:50:26PM +0530, Neeraj Upadhyay wrote: > >>If rcu_kick_kthreads is set, and gp is in progress, check_cpu_stall() > >>does checks to figure out whether jiffies is past rsp->jiffies_stall, > >>doing ordered accesses to avoid any false positives for new grace > >>period initialization after a sufficiently large idle period. This > >>extra processing can be skipped if rcu_cpu_stall_suppress is set. > >Just to make sure I understand, the concern is that someone might have > >booted with rcupdate.rcu_cpu_stall_suppress=1 (thus suppressing the RCU > >CPU stall debugging warnings implemented later in check_cpu_stall()), > >but later decided to also boot with rcutree.rcu_kick_kthreads=1 (thus > >enabling kicking kthreads which check for RCU's grace-period kthreads > >not being properly awakened)? > > > >My immediate reaction is that if there is not much point in specifying > >both rcutree.rcu_kick_kthreads=1 and rcupdate.rcu_cpu_stall_suppress=1. > >But is there some use case that I am missing? > > > > Thanx, Paul > For boot time configuration, agree, there isn't much point in enabling > both options. In addition to boot time, rcu_cpu_stall_suppress can > be temporarily enabled during some operations like sysrq; but this may > not be a use case worth consideration. OK, I will skip this one, for the time being at least. But thank you for your review and patches! Thanx, Paul > >>Fixes: 8c7c4829a81c ("rcu: Awaken grace-period kthread if too long since FQS") > >>Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> > >>--- > >> kernel/rcu/tree.c | 7 +++++-- > >> 1 file changed, 5 insertions(+), 2 deletions(-) > >> > >>diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > >>index 51d4c3a..91b7552 100644 > >>--- a/kernel/rcu/tree.c > >>+++ b/kernel/rcu/tree.c > >>@@ -1562,10 +1562,13 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) > >> unsigned long js; > >> struct rcu_node *rnp; > >> > >>- if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || > >>- !rcu_gp_in_progress(rsp)) > >>+ if (!rcu_gp_in_progress(rsp)) > >> return; > >> rcu_stall_kick_kthreads(rsp); > >>+ > >>+ if (rcu_cpu_stall_suppress) > >>+ return; > >>+ > >> j = jiffies; > >> > >> /* > >>-- > >>QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > >>member of the Code Aurora Forum, hosted by The Linux Foundation > >> > > -- > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a > member of the Code Aurora Forum, hosted by The Linux Foundation > ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2017-08-08 21:56 UTC | newest] Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2017-08-08 17:20 [PATCH] rcu: Skip additional checks if rcu_cpu_stall_suppress is set Neeraj Upadhyay 2017-08-08 18:02 ` Paul E. McKenney 2017-08-08 18:57 ` Neeraj Upadhyay 2017-08-08 21:56 ` Paul E. McKenney
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